Optimized design of four-zone phase pupil filter for nanoscale phase transition optical lithography

Abstract

The present paper describes a method for decreasing the pit size in optical lithography by using combination of a four-zone annular binary phase filter and the phase transition material. The binary phase filter was designed by vector diffraction theory when linearly polarized light is focused under high numerical aperture objective lens ( NA=0.95), the figures of merit produced by this filter are as follows: compared with the diffraction limited spot, Strehl ratio S is 0.254, the spot size in the short axis direction is reduced down to 77.3%, the depth of focus is elongated to 317% for the super-resolved spot,. Then a phase transition material is placed in the focal plane of the objective lens, according to the threshold effect of the material, the groove linewidth and pit size can decrease down to about 0.2λ, which is about 90nm at the wavelength of 405nm. Therefore, nanoscale phase transition optical lithography is realized, and the capacity and density of the optical memory devices can be increased up to 2-3 times the blu-ray disks.